To understand bladder cancer, it helps to know about the normal structure and function of the bladder.
The bladder is a hollow organ in the pelvis with flexible, muscular walls. Its main function is to store urine before it leaves the body. The average adult bladder holds about 2 cups of urine. Urine is made by the kidneys and is then carried to the bladder through tubes called ureters.
When you urinate, the muscles in the bladder contract, and urine is forced out of the bladder through a tube called the urethra. In women, the urethra is very short and opens just above the vagina. In men, the urethra is longer. It passes through the prostate gland and the penis, and opens at the tip of the penis.
The wall of the bladder has 4 main layers.
Knowing about these layers is important in understanding how bladder cancer grows. Most bladder cancers start in the urothelium. As the cancer grows into or through the other layers in the bladder, it becomes more advanced (see “How is bladder cancer staged?”) and harder to treat.
Bladder cancers are divided into several types based how their cells look under a microscope. Different types can respond differently to treatments such as radiation and chemotherapy.
This is by far the most common type of bladder cancer. About 95% of bladder cancers are this type. The cells from transitional cell carcinomas look like the urothelial cells that line the inside of the bladder.
Urothelial cells also line other parts of the urinary tract, such as the lining of the kidneys (called the renal pelvis), the ureters, and the urethra, so transitional cell cancers can also occur in these places. In fact, patients with bladder cancer sometimes have other tumors in the lining of the kidneys, ureters, or urethra. If someone has a cancer in one part of their urinary system, the entire urinary tract needs to be checked for tumors.
Bladder cancers are often described based on how far they have invaded into the wall of the bladder:
A bladder cancer can also be described as superficial or non-muscle invasive. These terms include both non-invasive tumors as well as any invasive tumors that have not grown into the main muscle layer of the bladder.
Transitional cell carcinomas are also divided into 2 subtypes, papillary and flat, based on how they grow.
If either a papillary or flat tumor grows into deeper layers of the bladder, it is called an invasive transitional cell (or urothelial) carcinoma.
Several other types of cancer can start in the bladder, but these are all much less common than transitional cell (urothelial) cancer.
Squamous cell carcinoma: In the United States, only about 1% to 2% of bladder cancers are squamous cell carcinomas. Under a microscope, the cells look much like the flat cells that are found on the surface of the skin. Nearly all squamous cell carcinomas are invasive.
Adenocarcinoma: Only about 1% of bladder cancers are adenocarcinomas. The cancer cells have a lot in common with gland-forming cells of colon cancers. Nearly all adenocarcinomas of the bladder are invasive.
Small cell carcinoma: Less than 1% of bladder cancers are small-cell carcinomas, which start in nerve-like cells called neuroendocrine cells. These cancers often grow quickly and typically need to be treated with chemotherapy like that used for small cell carcinoma of the lung.
Sarcoma: Sarcomas start in the muscle cells of the bladder, but they are rare. More information about sarcomas can be found in our documents:
These less common types of bladder cancer (other than sarcoma) are treated similar to transitional cell cancers, especially for early stage tumors, but different drugs may be needed if chemotherapy is required.
Last Medical Review: 11/15/2012
Last Revised: 01/17/2013
Referenced from American Cancer Society (cancer.org)